Present day recuperators and heat exchangers typically used a combination of metal component and ceramic components which must be bonded together. When using dissimilar materials, the joint therebetween is difficult to form, and the use of metal components has several major drawbacks. For example, metal components used in the recuperator or heat exchanger are susceptible to high temperatures and highly corrosive gases. Thus, the use of ceramic materials within recuperator and heat exchanger application to resist high temperature and high corrosive conditions has become necessary to provide longevity, serviceability and quality for future applications.
Additional problems are encountered in adapting ceramic material to high temperature heat exchangers. One of the biggest problem with present tube-type ceramic recuperators centers around the strength of the refractory used with header joints. Refractory materials are generally brittle. Specifically, composite ceramic-metal heat exchangers have problems attributable to stresses resulting from unlike thermal expansion characteristics of the diverse materials. The stresses can cause structural failure and fluid leakage between the high and low pressure sides of the heat exchanger. Additionally, present ceramic-metal heat exchangers are difficult to service and repair.
The increased use of ceramic materials has further emphasized the need for joining ceramic material to other ceramic materials. U.S. Pat. No. 4,784,313 which issued Nov. 15, 1988, to Jerzy Godziemba-Maliszewski, describes a method for bounding silicon carbide molded parts together or which ceramics or metal parts. The above patent discloses that SiC can be firmly bonded to itself or to molded bodies of other ceramic material or to metal work pieces by the establishment of diffusion-welding condition when a metal alloy layer is interposed between cleaned and polished surfaces.
In U.S. Pat. No. 4,642,864, issued Feb. 17, 1987 to Arthur G. Metcalfe et al., a joint construction for joining ceramic and metallic components for use in a recuperator or heat exchanger tube assembly is disclosed. The joint includes a bonding material cast between a ceramic tube and a metal member. The joint further has a seal member with sufficient ductility within a predetermined thermal operating range which will plastically deform and yet maintain an effective fluid seal between the ceramic and metal members.
In U.S. Pat. No. 5,265,918, issued Nov. 30, 1993 to Michael E. Ward and Bruce D. Harkins, a joint construction for joining ceramic to ceramic components for use in a recuperator or heat exchanger tube assembly is disclosed. The joint includes a refractory material disposed in a groove forming a mechanical locking device. The joint provides a high strength load bearing joint having good thermal cycling characteristics, good resistance to corrosive environment and good steady state strength at elevated temperatures.
The present invention is directed to overcoming one or more of the problems set forth above.